After a protracted clearance wrangle, McKellar joined Richmond for a reported $42,000 over two years after playing 74 senior games for Woodville in the SANFL, in which he won two best and fairests and a premiership as well as representing South Australia twice.

In 1972 he became a permanent fixture in the Tigers' side, finishing fourth in their Best and Fairest and earning ten Brownlow Medal votes. He continued to be a fixture at Richmond, even representing Victoria in 1975 before being dropped to the bench for their first finals match and then out of the side altogether.

After the snub he walked out on the Tigers and announced his retirement at 25 years old. He was Richmond's top vote getter in the Brownlow Medal that year and finished fifth in their Best and Fairest award. His retirement didn't last long and soon a number of clubs were circling him.

With Carl Ditterich having returned to St Kilda for cash and players Melbourne needed a ruckman and eventually landed McKellar despite the clearance being held up by a series of internal wrangles at Punt Road.

Richmond's president promised him to Footscray for $40,000 after a committeman had already made a deal with the Demons to trade him for $35,000. As a compromise the Tigers tried to offload him to South Melbourne but they decided not to enter a bid. Subiaco also lodged a bid but McKellar didn't consider the prospect of crossing to the WAFL.

He had already agreed terms with the Demons so it was no surprise that he chose to honor his deal and cross to Melbourne where he played three seasons before retiring after form struggles, injuries and increasing work commitments.